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Old 02-14-2011, 07:55 AM   #1
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Truck Shells and MPG

Hi - I have a 2006 Dodge Ram 2500 with 5.9L engine. This wonderful truck gets about 23.5 mpg in town and an astounding 30.3 mpg on the highway. I am not complaining.

The truck is currently equipped with a hard tonneau cover, which I am sure helps the mpg on the highway. I am planning to replace the tonneau cover with a fitted truck shell, probably a Snug-Top, ARE or Leer. The Snug-Top is most attractive because of its more aerodynamic rear end.

Does anybody know how this might affect highway mpg? I'm assuming that it will drop somewhat, but I would like to hear from other forum members who have converted their trucks to shells and what they experienced in mileage effects.
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Old 02-14-2011, 08:44 AM   #2
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Isn't that cummins the most wonderfull thing! If you're getting 30+ per US gallon, the world needs to know what you are doing. My 98 gets 26 to 27 per imperial gal empty and about 18 pulling the airstream. I don't think you'll notice any change if you go to a cap as long as it is even with the top of the cab. I think air resistance is more a product of frontal area. I remember seeing a test done with just the bed, tailgate on and tailgate off, there was no discernible difference.
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Old 02-14-2011, 09:32 AM   #3
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true, there is no difference, proved by many tests. i have owned a 96, 97, 03 and have 05 cummins 6sp 4x4. i have never seen that type of mileage. 19 mpg is the best i have ever got. have a brother inlaw gets 21mpg with a 96 cummins 2 wheel drive 5sp.
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Old 02-14-2011, 09:56 AM   #4
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30 MPG WOW I want one !!
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Old 02-14-2011, 10:11 AM   #5
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I suggest you run the reynolds numbers. I'm sure you will be surprised at your findings.
what I found with my drainpipe was that the awning supports at the rear of the trailer interrupted the laminar flow and actually reduced the turbulence behind the trailer thus increasing mpg. also of note was the disturbance around the rear vent, use of vortex generators applied here is something to think about,
BUT as far as towing goes-- the less amount of disturbance from the shell to the front of the trailer would be ideal.The truck is already cutting the hole in the atmosphere why do it again with the trailer? Use of yarn telltales as uses by sailors,gliders etc should help you devise an acceptable flow from shell to trailer. You may need a small air dam to improve this flow, or not.
anyway have fun.Let us know your findings.
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Old 02-14-2011, 01:11 PM   #6
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Thanks all for the info. I'll go with the smoothest shell I can find from one of the top manufacturers.

All good info too DoorGunner. (Love your Avitar).

Here's the story on the MPG. I did a lot of research before buying this truck. Found that inline 6 diesels get way better mpg than V8 diesels regardless of brand (just the facts). Found that the 5.9L Cummins gets much better mpg than the 6.7L Cummins. OK, go for the 5.9L. Found that 2005 to early 2007 5.9s get a little better mileage than earlier 5.9L engines. Found that diesels "get used to" the kind of duty they are put into and adapt their performance to suit that environment. I liked the 2006 cab design better than the 2005 or 2007. The 2500 was best suited to the 34' Airstream's weight (9800lbs). Bought the 2500 Laramie Bucket Seat version (just a beautiful cab design). Started looking for a truck that had mostly highway miles (the performance environment I wanted). I found this truck in Wisconsin. Bought it over the internet on photos and description of previous use. Drove it home from Wisconsin to South Texas at 65mph no cruise control (another mpg factor). As we pulled into the driveway, the mpg on the console read 30.3. Our cross-check to actual fuel vs. actual miles worked out to 30.1.

Like I said, no complaints.

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Old 02-14-2011, 02:31 PM   #7
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Secguru,
I'm betting you must have the manual transmission and 2wd truck. This setup always gets the best mileage. These generation 3 models are also some of the more sought after trucks as many of the bugs have been worked out and they were the pre 2007 emissions requirements. The 12 valve engines (pre 1998) are also sought after due to the simplicity of the injection system.
The 6.7 Cummins engine is very similar to the 5.9 of previous years except it has more power, quieter and but less fuel mileage due to the emissions and horse power wars. (Our 2009 4xd, Auto 6.7 CTD gets 11-13.5 mpg towing @ 70 mph and 18 mpg solo @ 70 mph)
Someday I hope the manufacturers understand that pre 2007 trucks had plenty of horsepower for most peoples needs and they need to concentrate on the fuel efficiency for future trucks.
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Old 02-14-2011, 02:44 PM   #8
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Secguru,
I'm betting you must have the manual transmission and 2wd truck. This setup always gets the best mileage. These generation 3 models are also some of the more sought after trucks as many of the bugs have been worked out and they were the pre 2007 emissions requirements. The 12 valve engines (pre 1998) are also sought after due to the simplicity of the injection system.
The 6.7 Cummins engine is very similar to the 5.9 of previous years except it has more power, quieter and but less fuel mileage due to the emissions and horse power wars. (Our 2009 4xd, Auto 6.7 CTD gets 11-13.5 mpg towing @ 70 mph and 18 mpg solo @ 70 mph)
Someday I hope the manufacturers understand that pre 2007 trucks had plenty of horsepower for most peoples needs and they need to concentrate on the fuel efficiency for future trucks.
That aint gonna happen as long as Unkle Sam is involved. Sal.
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Old 02-14-2011, 03:32 PM   #9
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30 MPG WOW I want one !!
me too, i'll trake my 05 cummins 6sp for one.
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Old 02-14-2011, 05:17 PM   #10
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use of vortex generators applied here is something to think about
How many volts should those vortex generators be?

Actually, I flew the F-86D many years ago and I do know what vortex generators are (see photo).
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Old 02-14-2011, 06:39 PM   #11
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The "Mythbusters" T.V. show did a field test to see if tailgate on/off and toppers changed fuel economy. I recall that the best MPG was simply with the tailgate up as the truck was designed, although when re-tested, the mesh tailgate helped. The MPG difference overall wasn't that significant between configurations.

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Old 02-14-2011, 06:58 PM   #12
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I'm from the Show Me State. Respectfully, I can't believe 30-plus MPG figures for a 3/4-ton truck irrespective of the year of the vehicle. I also can't believe 23-plus MPG figures for city driving for the same vehicle. Those are Honda Civic numbers.
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Old 02-14-2011, 07:59 PM   #13
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My 2001 Ram gets 12-14 mpg w/o a trailer. 5.9 gas, auto, 4wd. no truck cap. Our 1st trip with the Airstream, we got between 8.5 - 11 mpg. It may get lousy mpg's but with the Airstream in tow, we are doing it IN STYLE
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Old 02-14-2011, 10:11 PM   #14
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you're killing me

Quote:
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How many volts should those vortex generators be?

Actually, I flew the F-86D many years ago and I do know what vortex generators are (see photo).
leave it to you air force guys to crap in the mess gear
Semper Fi;

there are no fighter pilots down below, there are no fighter pilots down below,
oh that place is full of ----,navigators and bombadiers.
there are no fighter pilots down below.
thanks for your flight time
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